low estrogen

so i am doing ivf this month, had transfer of 4 embryos last thursday and had to go for bloodwork this monday and today, my pregnancy test will be next thursday,

so the drs office just calls and tells me my estrogen levels are borderline and they want me to take some pill 2x a day till next week

what does this mean, how does the estrogen level effect pregnancy,
i was feeling so positive this month and now i am scared